The present invention relates to a lens inclination adjustment system for adjusting an inclination of a lens, and more particularly, to a lens inclination adjustment system for adjusting an inclination of an objective lens in an optical system of a data recording/reproducing device.
Conventionally, a data recording/reproducing device using an optical disk as a recording medium has been known. Such a device is provided with an optical system which includes a light source, an objective lens held in a lens holder. A recording medium (i.e., an optical disk) is set at a focal point of the objective lens. The light source emits a parallel light beam which is focused by the objective lens to form a beam spot on the recording medium. The beam reflects off the recording medium, and is received by an optical pick-up device.
In the data recording/reproducing device, an optical axis of the objective lens preferably intersects the recording medium at right angles because, if the optical axis inclines with respect to a normal line to the recording medium, coma occurs, which may cause the beam spot formed on the recording medium to be wider than it should be. If the beam spot is wider, a density of recording to the recording medium will be lower. Further, if the beam spot is wider, a reproduced signal may include noise.
Recently, a numerical aperture NA of the optical system for such a device has become larger. In the device which has an optical system having relatively great numerical aperture NA, even a small inclination of the objective lens may greatly affect the size of the beam spot.
Accordingly, it is necessary to adjust the inclination of the object lens such that an inclination angle formed between the optical axis of the objective lens and a line normal to the recording medium is within a permissible range. The permissible range is, for example, a range within 3 minutes.
In order to adjust the inclination of the objective lens, conventionally, a lens inclination adjustment system is used. The conventional inclination adjustment system includes an interferometer unit and a lens inclination adjustment unit.
Firstly, at least a part of the data recording/reproducing device including the optical system and the light source is coupled with the interferometer unit, and interference fringes are observed. A user may determine the inclination angle and inclination direction which is a direction of inclination from a plane parallel to the surface of the recording medium or the cover glass facing the objective lens, based on the observed interference fringes.
Next, the data recording/reproducing device is coupled with the lens inclination adjustment unit, and the lens is moved so that the inclination (i.e., the inclination angle and inclination direction) is adjusted to be in a permissible range in accordance with the inclination angle and the inclination direction determined by the user.
When the inclination of the objective lens is thus adjusted, the part of the data recording/reproducing device is coupled to the interferometer unit again and the interference fringes are observed again. Until the inclination of the objective lens falls within the permissible range, the above process of observing the interference fringe patterns, determining the inclination angle and the inclination direction of the objective lens and changing the inclination of the objective lens is repeated.
Accordingly, it takes a long time to adjust the inclination of the objective lens. Further, the inclination direction and the inclination angle may not be sufficiently precisely detected if the observation of the interference fringes are carried out by sight. In such a case, it may be difficult to adjust the inclination of the object lens to fall within a permissible range with use of the conventional lens inclination adjusting system even if the above-described process is repeated.